DC plant controller and method for selecting among multiple power sources and DC plant employing the same

ABSTRACT

Various embodiments of a DC plant controller, methods of selecting among multiple power sources and DC plants incorporating the DC plant controller or the method. In one embodiment, the DC plant controller includes: (1) a source identifier configured to identify power sources couplable to a common DC bus, (2) a source prioritizer coupled to the source identifier and configured to prioritize the power sources based on at least one criterion and (3) an output characteristic assigner coupled to the source prioritizer and configured to assign output characteristics to the power sources that differ from one another as a function of the priority.

TECHNICAL FIELD

This application is directed, in general, to plant controllers and, morespecifically, to a DC plant controller, a method for selecting amongmultiple power sources and a DC plant employing the controller or themethod.

BACKGROUND

Conventionally, a telecommunication or other DC-based power plantemploys multiple AC or DC power sources to provide a regulated DCvoltage to a load. AC power sources use rectifiers to convert their ACoutput voltages to a regulated DC output, and DC power sources use DC-DCconverters to adjust their voltages to a regulated DC output. A DC busaggregates the DC outputs, allowing them to power the load. A centralcontroller controls the rectifiers and converters to allocate the loadamong the multiple power sources. Sometimes a single power source bearsthe load, but more often multiple power sources share the load to someextent. Various techniques have been devised to achieve load sharingamong multiple power sources. U.S. Pat. No. 5,740,023, which issued toBrooks, et al., on Apr. 14, 1998, entitled “Control System for a ModularPower Supply and Method of Operation Thereof” and commonly assigned withthis application describes several conventional load-sharing techniqueand introduces a novel technique particularly suited for use withmodular power supplies of nominally the same type and rating.

SUMMARY

One aspect provides a DC plant controller. In one embodiment, the DCplant controller includes: (1) a source identifier configured toidentify power sources couplable to a common DC bus, (2) a sourceprioritizer coupled to the source identifier and configured toprioritize the power sources based on at least one criterion and (3) anoutput characteristic assigner coupled to the source prioritizer andconfigured to assign output characteristics to the power sources thatdiffer from one another as a function of the priority.

Another aspect provides a method of selecting among multiple powersources couplable to a common DC bus. In one embodiment, the methodincludes: (1) identifying the power sources, (2) prioritizing the powersources based on at least one criterion and (3) assigning outputcharacteristics to the power sources that differ from one another as afunction of the priority.

Yet another aspect provides a DC plant. In one embodiment, the DC plantincludes: (1) power sources couplable to a common DC bus and selectedfrom the group consisting of: (1a) an engine-driven generator, (1b) awindmill-driven generator, (1c) a solar array and (1d) AC mains; (2)rectifiers and DC-DC converters associated with the power sources and(3) a DC plant controller, including: (3a) a source identifierconfigured to identify the power sources, (3b) a source prioritizercoupled to the source identifier and configured to prioritize the powersources based on at least one criterion and (3c) an outputcharacteristic assigner coupled to the source prioritizer and configuredto assign output characteristics to the power sources that differ fromone another as a function of the priority and assign power limits toones of the rectifiers and the DC-DC converters.

BRIEF DESCRIPTION Reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of one embodiment of a plant employing a DCplant controller or a method constructed or carried out according to theprinciples of the invention;

FIG. 2 is a block diagram of one embodiment of a DC plant controllerconstructed according to the principles of the invention; and

FIG. 3 is a flow diagram of one embodiment of a method of selectingamong multiple power sources and controlling a plant carried outaccording to the principles of the invention.

DETAILED DESCRIPTION

As stated above, various conventional techniques have been devised toachieve load sharing among multiple power sources. However, conventionalplants tend to use power sources that are predominantly of the samegeneral type to provide primary DC power. For example, most plants useparallel rectifiers to provide primary DC power. They may differ interms of their rated capacity but otherwise function identically.However, with the increasing interest and usage of alternative powersources, it is becoming necessary to provide a mechanism for atelecommunication or other DC-based power system to be able toaccommodate multiple power sources that differ, perhaps fundamentally,in type, to provide primary DC power. More often than not one powersource is unable to provide the full power a load requires. Thus,multiple power sources may need to be used concurrently to providestable operation. What is needed is a system or a method for selectingthe proper power sources from the power sources that are available at agiven point in time to provide primary DC power.

With the benefit of the teachings herein, DC plants may benefit from avariety of different types of power sources in terms of overalloperating efficiency, reliability or environmental desirability. DCplants may also be located in relatively remote areas, where connectionto the commercial power grid is problematic. DC plants may also takeadvantage of emerging (e.g., relatively “green”) power sources, whichmay operate more sporadically than more conventional power sources. ThusDC plants may be associated with geographically dispersed facilities ofall kinds, including central offices (COs), cellular base stations,Digital Subscriber Line (DSL), fiber optical, radio and microwaverepeaters, routers, gateways and Customer Premises Equipment (CPE).

FIG. 1 is a block diagram of one embodiment of a plant employing a plantcontroller or a method constructed or carried out according to theprinciples of the invention. The plant includes one or more AC powersources and one or more DC power sources and corresponding equipment toprovide suitable primary DC power. In the specific embodiment of FIG. 1,the plant includes a first AC power source 110, a second AC power source120 and a first DC power source 130. The first AC power source 110provides its AC output to a first rectifier 140 that includes a first ACtransducer 141 and a first rectifier controller 142 and provides aregulated DC output. The second AC power source 120 provides its ACoutput to a second rectifier 150 that includes a second AC transducer151 and a second rectifier controller 152 and provides a regulated DCoutput. The first DC power source 160 provides its DC output to a firstDC-DC converter 160 that includes a converter controller 161 andprovides a regulated DC output. The first AC power source 110, thesecond AC power source 120 and first DC power source 130, acting throughtheir respective first rectifier 140, second rectifier 150 and firstDC-DC converter 160 are coupled to positive and negative rails of acommon DC bus 170 and selectably provide primary DC power to the DC bus170. One or more batteries or capacitors 180 are also coupled to the DCbus 170 to provide secondary DC power to the extent that the firstrectifier 140, the second rectifier 150 and the first DC-DC converter160 are unable to provide sufficient primary DC power. In oneembodiment, the one or more batteries or capacitors 180 include one ormore battery strings. In another embodiment, the one or more batteriesor capacitors 180 include one or more large, “super” capacitors. A load190 is coupled to the DC bus 170 and consumes the DC power provided byone or more of the first rectifier 140, the second rectifier 150, thefirst DC-DC converter 160 and the one or more batteries or capacitors180. The load may be telecommunication equipment, computer equipment,equipment of any kind whatsoever (including recharging equipment for theone or more batteries or capacitors 180) or any other kind ofconventional or later-developed load.

In one embodiment, the first rectifier 140, the second rectifier 150 andthe first DC-DC converter 160 are rack-mountable and occupy one or moreshelves of a standard rectifier/converter rack. In another embodiment,the first rectifier 140, the second rectifier 150 and the first DC-DCconverter 160 are joined together with other rectifiers and converters(not shown) to form bays of rectifiers and converters. The latterembodiment is more typically associated with a very large DC plant.

A DC plant controller 200 is coupled to the first rectifier 140, thesecond rectifier 150 and the DC-DC converter 160 to monitor, control orboth monitor and control the same. In the illustrated embodiment, the DCplant controller 200 is also coupled to the first AC power source 110,the second AC power source and the first DC power source 130 to monitor,control or both monitor and control the same. One or more data links maybe employed to allow this monitoring or control. A first unreferenceddata link couples the power sources, namely the first AC power source110, the second AC power source 120 and the first DC power source 130,to the DC plant controller 200. In one embodiment, the first data linkis a serial data link. In another embodiment, the first data link is abidirectional link. The first data link or another, second unreferenceddata link also couples the first rectifier 140, the second rectifier 150and the first DC-DC converter 160 to the DC plant controller 200. In oneembodiment, the data link is a serial data link. In another embodiment,the data link is a bidirectional link.

In general, the DC plant controller 200 is configured to assign outputcharacteristics to the various power sources based on a priority. Theoutput characteristics differ from one another. For example, the powersource assigned the highest output voltage provides power to the load190 until (1) it enters a current-limiting mode of operation in whichits output voltage begins to drop in order to limit output current or(2) its output voltage begins to drop naturally. When its output voltagereaches that assigned to the power source having the second highestpriority, the two power sources begin to share the load 190. If the load190 remains or becomes so large that both power sources operate incurrent-limiting mode, a power source having a third highest prioritybegins to share, and so on. The DC plant controller 190 mayincrementally raise the output voltage of some of the power sources tomaintain the voltage of the DC bus 170 close to the output voltageoriginally assigned to the power source having the highest priority toensure that maximum utilization power from that power source isachieved. Should the load 190 decrease, power sources exit the currentsharing mode and contribute less to load-sharing in reverse priorityorder.

For example if the bus 170 needs to be at 54V to keep the one or morebatteries or capacitors 180 charged, and a solar array has the highestpriority, its output voltage will be assigned to be 54 volts. The nextpriority power source is assigned an incrementally lower output voltage,and so forth. If the solar array is unable to bear the load 190, itsoutput voltage will drop down to the voltage level of the next powersource. The DC plant controller 200 can then incrementally raise theoutput voltage to be as close as possible to the required 54 volts,while maintaining the solar array power source in a current limit modeto ensure that maximum utilization of solar energy is achieved.

One embodiment of the DC plant controller 200 constructed according tothe principles of the invention will now be described in conjunctionwith FIG. 2. The DC plant controller 200 includes a source identifier210. The illustrated embodiment of the source identifier 210 isconfigured to identify power sources (e.g., the first AC power source110, the second AC power source and the first DC power source 130 ofFIG. 1) couplable to a common DC bus (e.g., the DC bus 170 of FIG. 1).For example, if the first AC power source 110 or the second AC powersource 120 is an engine-driven generator, a windmill-driven generator, awater-driven generator, a geothermally driven generator or AC mains(i.e., leading from a commercial power grid), the source identifier 210identifies it as such. As another example, if the first DC power source130 is a solar array or a battery, the source identifier 210 identifiesit as such. In one embodiment, the source identifier 210 is configuredto receive data indicating the identity of a power source from a memoryassociated with the power source or a database separate from the powersource. In another embodiment, the source identifier 210 is configuredto identify the power source based on the characteristics of the powerit produces. For example, the power produced by a windmill-drivengenerator varies in frequency and voltage as a function of windmillspeed, while the power produced by a solar array varies in amperageroughly as a function of the time of day. The power produced by otherpower sources may likewise have characteristics that allow a properlyconfigured source identifier to identify them.

Identifying the power sources provides a basis for prioritizing them.Accordingly, the DC plant controller 200 also includes a sourceprioritizer 220. The illustrated embodiment of the source prioritizer220 is coupled to the source identifier 210 and is configured toprioritize the power sources based on at least one criterion.

In one embodiment, the criterion is operational cost, namely the cost tooperate each of the identified power sources (e.g., taking into accountfuel or electricity costs). In a more specific embodiment, the sourceprioritizer 220 gives a power source having a lower operational cost ahigher priority than a power source having a higher operational cost.

In another embodiment, the criterion is a “carbon footprint,” which is ametric used nowadays to gauge the environmental impact of operating eachof the identified power sources. In a more specific embodiment, thesource prioritizer 220 gives a power source having a smaller carbonfootprint a higher priority than a power source having a larger carbonfootprint.

In yet another embodiment, the criterion is noise generation, namely thenoise generated operating of each of the identified power sources. In amore specific embodiment, the source prioritizer 220 gives a powersource that generates less noise a higher priority than a power sourcethat generates more noise.

In still another embodiment, the criterion is a combination of powersources selected. For example, if a windmill-driven generator is given ahighest priority, a highly reliable power source, such as AC mains, maybe given the next highest priority given the unpredictable nature ofwindmill operation. If a solar array is given a highest priority, anengine-driven generator may be given the next highest priority given thepredictable decline in solar array output that occurs at dusk.

In yet still another embodiment, the criterion is an environmentalfactor, such as time of day, time of year, sunlight level ortemperature. For example, a windmill-driven generator may be given a farhigher priority during the day, when winds are typically higher, than atnight, when winds tend to be calmer. A solar array may be given a higherpriority during the summer than during the winter. An engine-drivengenerator may be given a higher priority during the day than at night,when neighbors are asleep, but perhaps not as high during a relativelyhot day, when its operating temperature may become excessive. Thoseskilled in the pertinent art will readily see a vast array of possiblecriteria upon which priority may be based, including any combination ofthe above or other criteria.

The DC plant controller 200 further includes a sources and prioritiesdatabase 230. The sources and priorities database 230 is coupled to thesource prioritizer 220. In one embodiment, the sources and prioritiesdatabase 230 is configured to store data pertaining to the identity ofthe power sources in the DC plant that the source identifier 210 mayemploy to identify the power sources. In another embodiment, the sourcesand priorities database 230 is configured to store data pertaining toone or more criteria that the source prioritizer 220 may employ toprioritize the power sources.

The DC plant controller 200 further includes an output characteristicassigner 240. The illustrated embodiment of the output characteristicassigner 240 is coupled to the source prioritizer 230 and is configuredto assign one or more output characteristics to the power sources thatdiffer from one another as a function of the priority. In oneembodiment, the output characteristics may include output voltages,power limits or current limits or current share thresholds. In a morespecific embodiment, the output characteristics consist of outputvoltage. In an alternative, more specific embodiment, the outputcharacteristics consist of current share/current limit/power limitthresholds (i.e., setpoints). In another embodiment, the sources andpriorities database 230 is configured to make the data pertaining to oneor more criteria that the source prioritizer 220 may employ toprioritize the power sources available to the output characteristicassigner 240 to effect assignment of the output characteristics.

In one embodiment, the output voltages differ by less than one volt anddecrease as the priority decreases. For example, the output voltage ofthe power source given the highest priority may be assigned to be −24.0volts. The output voltage of the power source given the second highestpriority may be assigned to be −23.7 volts. The output voltage of thepower source given the third highest priority may be assigned to be−23.5 volts.

In another embodiment, the output voltages differ by less than aboutfive volts and decrease as the priority decreases. For example, theoutput voltage of the power source given the highest priority may beassigned to be +54 volts. The output voltage of the power source giventhe second highest priority may be assigned to be +53 volts. The outputvoltage of the power source given the third highest priority may beassigned to be +51 volts.

In yet another embodiment, the output voltages differ by less than aboutten volts and decrease substantially linearly as the priority decreases.For example, the output voltage of the power source given the highestpriority may be assigned to be −48 volts. The output voltage of thepower source given the second highest priority may be assigned to be −46volts. The output voltage of the power source given the third highestpriority may be assigned to be −44 volts.

In the context of FIG. 1, the output characteristic assigner 240 isconfigured to assign power limits to the first AC power source 110, thesecond AC power source and the first DC power source 130 by assigningpower limits to their corresponding first rectifier 140, secondrectifier 150 and first DC-DC converter 160. In one embodiment, thesource identifier 210 is configured to communicate with the powersources via the first data link of FIG. 1, and the output characteristicassigner 240 is configured to communicate with the power sources via thesecond data link of FIG. 1. In certain embodiments, the outputcharacteristic assigner 240 is further configured to calculate theholdup time of the one or more batteries or capacitors 180 of FIG. 1 andplace ones of the power sources on standby based on the calculatedholdup time.

As stated above, one or more criteria may be employed to prioritizeamong the power sources. Accordingly, the DC plant controller 200 mayinclude a timer 260 configured to provide information regarding, e.g.,time of day or time of year, which may be useful if time is a criterion.The DC plant controller 200 may include a microphone 270 configured toprovide a signal indicating noise, which may be useful if noise is acriterion. The DC plant controller 200 may include a temperature sensor280 configured to provide a signal indicating a temperature, which maybe useful if operating or ambient temperature is a criterion. The DCplant controller 200 may include a history database 250 configured tostore data regarding the past operation of the DC plant. In oneembodiment, the source prioritizer 220 is configured to factorhistorical data into future prioritization decisions. For example, if aparticular DC plant is located in a particularly cloudy area, its solararray may prove less effective over time and therefore merit beingassigned a lower priority.

FIG. 3 is a flow diagram of one embodiment of a method of selectingamong multiple power sources and controlling a plant carried outaccording to the principles of the invention. In various embodiments,the power sources may include one or more of: an engine-drivengenerator, a windmill-driven generator, a solar array and AC mains.

The method begins in a start step 305. In a step 310, the power sourcesare identified. The identifying may be carried out as described above.In a step 315, the power sources are prioritized based on at least onecriterion. In various embodiments, the at least one criterion mayinclude one or more of: operational cost, carbon footprint, noisegeneration, a combination of power sources selected and an environmentalfactor.

In the embodiment of FIG. 3, the identities and priorities are storedfor later use. Accordingly, in a step 320, the identities and prioritiesare stored in a database. In analog systems, the identities andpriorities may be implemented using switches, jumpers or other hardwareelements. Also in the embodiment of FIG. 3, rectifiers, DC-DC convertersor a combination thereof are associated with the power sources.

In a step 325, output voltage, power limit/current limit and/or currentshare are assigned to the individual rectifiers and/or converters basedon priority of their powering source. In one embodiment, the sequence isoutput voltage followed by power/current limit followed by current sharethreshold. Other sequences are employed in alternative embodiments.

The output voltage may differ from one another as a function of thepriority. In one embodiment, the output voltages differ by less thanone-tenth of a volt and decrease as the priority decreases. In anotherembodiment, the output voltages differ by less than one volt anddecrease as the priority decreases. In yet another embodiment, theoutput voltages differ by less than about ten volts and decreasesubstantially linearly as the priority decreases. When used withbatteries or other energy storage devices or when used with voltagesensitive loads, the output voltage assigned to the rectifiers and/orconverters may be identical.

The power/current limit values assigned to rectifiers or converters maydiffer from one another as a function of the priority of their poweringsource. In one embodiment, the power/current limit values for thehighest priority source is set to 100% and then decremented by fixed orvarying amounts as the priority decreases. In another embodiment, thepower/current limit values for the highest priority source is set below100% and then decremented by fixed or varying amounts as the prioritydecreases. In yet another embodiment, the power/current limit values areidentical for all the power sources.

The current share values assigned to rectifiers or converters may differfrom one another as a function of the priority of their powering source.Current sharing can be implemented through an analog bus where each unitcompares its output to a reference signal based on the outputs of otherunits; or through a digital scheme where the DC plant controllermeasures/calculates the overall output of the plant and assignsadjustments to rectifier voltage and/or current limit values through adigital bus. In one embodiment with the analog current share bus, therectifiers or converters with the lowest priority are inhibited fromadjusting their settings for a large or indefinite increment of time.The rectifier/converters with the highest priority are allowed torespond to the current share reference bus instantaneously and have ahigher current/power limit setting. In another embodiment, using adigital bus for current share, the controller adjusts the outputs of therectifiers such that the high priority rectifiers or converters areloaded the most and the low priority units are lightly loaded. Dependingon the digital scheme employed for current sharing, one such way isthrough the adjustment of the outer voltage loop in magnitudes of lessthan 0.01V. Larger voltages may be covered by the output voltagesetting.

In a step 330 one or more of the power sources or rectifiers orconverters associated with the power source are placed on standby basedon a calculated battery holdup time. The steps 310-330 may be repeatedin whole or in part occasionally or periodically as desired based on theneeds of a particular DC plant. The method ends in a step 335.

Those skilled in the art to which this application relates willappreciate that other and further additions, deletions, substitutionsand modifications may be made to the described embodiments.

1. A DC plant controller, comprising: a source identifier configured toidentify power sources couplable to a common DC bus; a history databaseconfigured to store history data regarding the past operation of a DCplant controlled by said DC plant controller; a source prioritizercoupled to said source identifier and said history database andconfigured to prioritize said power sources based on at least onecriterion and said history data; and an output characteristic assignercoupled to said source prioritizer and configured to assign outputcharacteristics to said power sources that differ from one another as afunction of said priority, and to place ones of said power sources onstandby based on a calculated battery holdup time.
 2. The DC plantcontroller as recited in claim 1 wherein said output characteristicsdiffer by less than one volt and decrease as said priority decreases. 3.The DC plant controller as recited in claim 1 wherein said outputcharacteristics differ by less than about five volts and decrease assaid priority decreases.
 4. The DC plant controller as recited in claim1 wherein said output characteristics differ by less than about tenvolts and decrease substantially linearly as said priority decreases. 5.The DC plant controller as recited in claim 1 wherein said power sourcesare selected from the group consisting of: an engine-driven generator, awindmill-driven generator, a solar array, and AC mains.
 6. The DC plantcontroller as recited in claim 1 wherein said at least one criterion isselected from the group consisting of: operational cost, carbonfootprint, noise generation, types of said power sources, and anenvironmental factor.
 7. The DC plant controller as recited in claim 1wherein rectifiers and DC-DC converters are associated with said powersources and said output characteristic assigner is further configured toassign power limits to one or more of said rectifiers and said DC-DCconverters.
 8. The DC plant controller as recited in claim 7 whereinsaid source identifier is configured to communicate with said powersources via a first bidirectional link and said output characteristicassigner is configured to communicate with said power sources via asecond bidirectional link.
 9. A method of selecting among multiple powersources couplable to a common DC bus, comprising: identifying said powersources; storing history data regarding past operation of said powersources; prioritizing said power sources based on at least one criterionand said history data; assigning output characteristics to said powersources that differ from one another as a function of said priority, andplacing ones of said power sources on standby based on a calculatedbattery holdup time.
 10. The method as recited in claim 9 wherein saidoutput characteristics differ by less than one volt and decrease as saidpriority decreases.
 11. The method as recited in claim 9 wherein saidoutput characteristics differ by less than about five volts and decreaseas said priority decreases.
 12. The method as recited in claim 9 whereinsaid output characteristics differ by less than about ten volts anddecrease substantially linearly as said priority decreases.
 13. Themethod as recited in claim 9 wherein said power sources are selectedfrom the group consisting of: an engine-driven generator, awindmill-driven generator, a solar array, and AC mains.
 14. The methodas recited in claim 9 wherein said at least one criterion is selectedfrom the group consisting of: operational cost, carbon footprint, noisegeneration, types of said power sources, and an environmental factor.15. The method as recited in claim 9 wherein rectifiers and DC-DCconverters are associated with said power sources and said methodfurther comprises assigning power limits to ones of said rectifiers andsaid DC-DC converters.
 16. The method as recited in claim 15 furthercomprising communicating identities from said power sources to saidsource identifier via a first bidirectional link and communicatingoutput characteristic and power limit commands from said outputcharacteristic assigner to said power sources, said rectifiers and saidDC-DC converters via a second bidirectional link.